Bidens frondosa L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Annual, generally glabrous or nearly so, 2–12 dm; lvs on petioles 1–6 cm, pinnately compound, with 3–5 lanceolate, acuminate, serrate lfls to 10 × 3 cm, sometimes sparsely short-hairy beneath, at least the terminal one slender-petiolulate; heads campanulate to hemispheric, or narrower in depauperate plants, discoid or nearly so, the disk to 1 cm wide in fl; outer invol bracts 5–10, typically 8, green and ± leafy, usually conspicuously surpassing the orange disk, evidently ciliate on the margins, at least toward the base; anthers exserted; achenes flat, narrowly cuneate, strongly 1-nerved on each face, commonly dark brown or blackish, subglabrous or appressed-hairy, 5–10 mm; pappus of 2 retrorsely (seldom antrorsely) barbed awns; 2n=24, 36, 48, 72. Waste places, especially in wet soil; Nf. and N.S. to Wash., s. to Ga., La., and Calif. June–Oct.